This invention relates to multiplexers of microwave electromagnetic signals which differ in frequency and, more particularly, to a multiplexer having a plurality of channels tuned to specific frequencies, each channel including a filter for coupling both transverse-electric (TE) and transverse-magnetic (TM) waves to shape a bandpass characteristic with steeper skirts to allow for a closer spaceing of contiguous signal bands.
Microwave multiplexers are employed in a variety of communication systems ranging from radar to telemetry. For example, in the case of a satellite carrying two highly directive antennas for receiving two signals at different frequency bands, the two signals received from the respective antennas are advantageously combined via a microwave multiplexer. The multiplexer outputs the two signals in a common channel of broader bandwidth. Thereby, a single microwave channel receives both of the signals. Such a multiplexer may be reciprocal in its operation such that a plural-band signal traversing the multiplexer in the reverse direction can be split into two separate signals each having its own spectral transmission band. If desired, such multiplexers may be constructed to accommodate more than two spectral bands. It is advantageous if the various bands can be placed together as closely as possible so as to reduce the required bandwidth of the common output channel of the multiplexer.
A problem arises in that, in the past, the bandpass characteristic of the resonant structure in each of the channels of the multiplexer has had wider skirts than is desireable, the excess width of the skirts necessitating additional spacing between contiguous ones of the signal bands to ensure adequate channel separation. This reduces the number of separate signal channels that can be combined into a single output channel of prescribed bandwidth.